Associate Attorney General Jane Young said Tuesday that the investigation is ongoing, and investigators are trying to determine what caused the fire and explosion. She said two bodies were found in the wreckage, Arkell's and the suspected shooter's, Michael Nolan, 47.

Young said Arkell arrived at the home about 4:10 p.m. after someone called to report a loud argument. He asked Michael Nolan's father, Walter Nolan, 86, if he could enter the home, and once he did, he was almost immediately fired upon, Young said.

About five minutes later, Fremont Officer Derek Franek arrived at the house. Young said Franek heard there were reports of gunfire before he arrived, and he found Walter Nolan outside the home. When Walter Nolan was unable to answer his questions, Franek handcuffed him as a precaution and left him outside.

Young said Franek went inside and saw that a wall had been sprayed with bullets. He found Arkell on his back in the house and was able to determine that he was likely dead. Franek was then fired upon and ran toward the back of the house, where he was able to escape off a deck, Young said.

"The courage that (Franek) had to walk into that situation alone, try to do what he could to help his fellow officer get out and then call for backup is heroic," Young said.

Young said other departments began arriving at the scene, and more gunshots were reported coming from the house. She said police didn't return fire because they didn't have a target to shoot.

By 4:47 p.m., fire was seen coming from the house. Seacoast Emergency Response and a SWAT team went near the home and were able to get Walter Nolan out of the front yard. He was treated for minor injuries and released into the care of family.

At 5:49 p.m., an explosion rocked the neighborhood and blew out a part of the home's roof. Young said the building was a duplex, and the resident in the other part of the structure had been able to get out safely earlier.

Young said Arkell had no indication of the danger he was in when he went to the home.

"It certainly seemed that Officer Arkell walked into a situation that he didn't anticipate," she said. "This is a pretty quiet town. It's 4 o'clock on a Monday. As someone said, this doesn't happen here."

Arkell was a married father of two teenage girls. Young said the family has asked for privacy.

"Words cannot describe the pain that they have," she said.

Investigators with the state Fire Marshal's Office, the Bureau of Alcohol, Tobacco, Firearms and Explosives and New Hampshire State Police are determining whether the wreckage of the building is safe to allow other investigators in. Young said there's no indication what caused the fire and explosion, although she said it's likely the fire was intentionally set, rather than accidental.

She said Michael and Walter Nolan had no criminal records or any motor vehicle violations she could find. The ATF is checking on any gun licenses issued to either of the men as well, Young said. She noted that Walter Nolan is not suspected of any wrongdoing.

An autopsy on Michael Nolan did not reveal a cause of death. Attorney General Joseph Foster said said more investigation is needed before a cause of death can be determined.

Streets leading to Mill Pond Road remained closed Tuesday as the investigation continued.

Timeline: Explosion rocks Brentwood home after murder of officer

1 of 17

Stephen Arkell

Brentwood Police Officer Stephen Arkell was shot and killed on May 12 at a home in the town shortly before the home went up in flames and exploded.

OFFICER ARKELL. JEAN MACKIN STARTS US OFF WITH THE VERY LATEST FROM BRENTWOOD. WELL, TODAY INVESTIGATORS CONFIRMED THAT OFFICER ARKELL WAS SHOT SEVERAL TIMES BEFORE THE FIRE EVEN STARTED AT THE HOUSE HERE IN BRENTWOOD. THEY PAINT A MINUTE BY MINUTE PICTURE OF WHAT HE FACED HERE YESTERDAY. 402 MONDAY AFTERNOON A NEIGHBOR CALLED 911, REPORTING A VERBAL DISPUTE ON MILL POND ROAD A HOUSE WHERE 47-YEAR-OLD MICHAEL NOLAN LIVED WITH HIS 86-YEAR-OLD FATHER, WALTER. OVERS STEPHEN ARKELL ARRIVED AT 4:10. THE FATHER GAVE HIM PERMISSION TO COME INSIDE. THERE WAS NO CRIMINAL HISTORY AT THE HOME, WHERE OFFICER ARKELL WAS MET WITH GUNFIRE. ALMOST IMMEDIATELY WITNESSES INDICATE THAT THEY HEAR WHAT IS DESCRIBED AS THREE VOLLEYS OF GUNFIRE. POLICE SAY THE 15-YEAR VETERAN OF THE BRENTWOOD POLICE DEPARTMENT, THE HUSBAND AND FATHER, WAS SHOT MULTIPLE TIMES. FOUR MINUTES AFTER OFFICER ARKELL ARRIVED, FREMONT OFFICER FRANTIC REACHED THE DUPLEX. WHEN HE WENT IN HE NOTICED A WALL HAD BEEN SPRAYED WITH BULLETS AND HE SAW OFFICER ARKELL ON THE FLOOR, ON HIS BACK. HE WALKED TOWARD HIM AND SAW THAT OFFICER ARKELL SUSTAINED WHAT WAS LATER TO BE DETERMINED TO BE A FATE INJURY. GUNFIRE THEN DROVE THE FREE MONTH OFFICER OUT THE BACK OF THE HOUSE TO SAFETY IN THE TREE LINE. AT 4:47 THE FIRST REPORTS OF SMOKE RISING FROM THE DUPLEX. ONE HOUR LATER. THE MASSIVE EXPLOSION. TWO BODIES WERE LATER RECOVERED, INCLUDING OFFICER STEPHEN ARKELL. LEAVING HIS POLICE DEPARTMENT, HIS HOME TOWN, IN HEARTBREAKING SHOCK. STEVE ARKELL MEANT A LOT TO MY DEPARTMENT, STEVE ARKELL WAS INVOLVED IN ANYTHING THAT HE COULD DO, HE WAS THERE TO DO IT. RIGHT NOW INVESTIGATORS BELIEVE THAT INITIAL FIRE WAS SET. THEY SUSPECT THAT PROPANE THAT FUELS THE HOME MAY HAVE SPARKED THE MASSIVE EXPLOSION, BUT THEY CAN'T CONFIRM THAT YET. INVESTIGATORS PLAN TO BE HERE ON THE SCENE OF THE HOUSE HERE IN BRENTWOOD THROUGH AT LEAST FRIDAY.

The Obama administration will unveil a major climate change plan Monday aimed at a large reduction in greenhouse gas emissions from the nation's coal-burning power plants, a senior administration official told CNN.